1. Field of the Invention
The present invention relates generally to the field of surface to down hole communication techniques for an oil rig. The invention pertains in particular to a direct interface which intercepts existing commands going to existing oil rig equipment and superimposing additional commands onto the existing commands to manipulate drilling mud pressure and/or other physically perceptible influences which a down hole tool or other device can detect and interpret.
2. Background of the Related Art
Varying mud pressure to command a down hole tool is well known in the art. Currently known techniques for manipulating mud pressure to communicate a command from the surface to down hole equipment are inefficient. These known mud pressure command systems require large, heavy equipment to be added to the oil rig to manipulate mud pressure. One example of a known mud pressure command system is the Halliburton Geo-Span™ downlink system. The Geo-Span™ system diverts mud flow to reduce mud pressure to change the azimuth and inclination of a steerable drilling system. The Geo-Span™ system requires the addition of a bulky high pressure mud diversion valve and controller. Such an addition is expensive and requires the utilization of additional rig space which is at a premium. Thus, there is a need for a down hole communication system that does not require the addition of the bulky mud diversion valve to existing equipment.
Some systems require operator to manually switch the mud pump on and off to create a pressure fluctuation. This pressure fluctuation is used to signal or command a down hole device which senses a change in the mud pressure. This manual technique is slow (on the order of several minutes to transmit a simple command). Moreover, these manual commands are subject to error due to the variation between operators' implementations of the manual commands. Thus, there is a need for a faster and more precise communication method and apparatus for communicating with down hole equipment.